The incidence of a tax rests on the person(s) whose real net income is reduced by the tax. It is fundamental that the real burden of taxation does not necessarily rest upon the person who is legally responsible for payment of the tax. General sales taxes are paid by business firms, but most of the cost of the tax is actually passed on to those who buy the goods that are being taxed. In other words, the tax is shifted from the business to the consumer. Taxes may be shifted in several directions. Forward shifting takes place if the burden falls entirely on the user, rather than the supplier, of the commodity or service in question—e.g., an excise tax on luxuries that increases their price to the purchaser. Backward shifting occurs when the price of the article taxed remains the same but the cost of the tax is borne by those engaged in producing it—e.g., through lower wages and salaries, lower prices for raw materials, or a lower return on borrowed capital. Finally, a tax may not be shifted at all—e.g., a tax on business profits may reduce the net income of the business owner.

Tax capitalization occurs if the burden of the tax is incorporated in the value of long-term assets—e.g., a decline in the price of land that offsets an increase in property taxes. Capitalization can result where there is forward shifting, backward shifting, or no shifting. Thus, an increase in the price of gasoline resulting from higher motor fuel taxes may reduce the value of high-consumption automobiles, a tax on the production of coal that cannot be shifted forward would reduce the value of coal deposits, and a tax that reduces after-tax corporate profits may reduce the value of corporate stock. In all these cases the present owner of the asset takes a capital loss because the value of the asset will be lower by the capitalized value of the tax.

It can be difficult to determine the incidence of a tax; indeed, the tax may be partly borne by the taxpayer and partly shifted. In many cases the problem can be adequately resolved by using what economists call partial equilibrium analysis, which involves focusing on the market for the taxed product and ignoring all other markets. For example, if a small tax were to be imposed on an addictive substance, there is little doubt that it would be borne by the users of the substance, who would pay the tax rather than forgo use of the substance. More generally, the incidence of taxation depends on all of the market forces at work. In a market economy the introduction of any tax triggers a whole series of adjustments in consumption, production, the supply of productive factors, and the pattern of foreign trade. These adjustments in turn will have repercussions on the prices of various commodities, productive factors, and assets that may be far removed from the area of the initial impact. In other words, a tax levied on a certain object may affect the prices of nontaxed goods and services that are not even used in the production of the object. Thus, the initial impact of a tax does not indicate where the ultimate burden will rest unless one knows what repercussions the tax will have throughout the system of interrelated economic variables—i.e., unless recourse is made to what is called general equilibrium theory, a method of analysis that attempts to identify and incorporate the economy-wide repercussions and implications of taxation. In what follows, an attempt will be made to isolate some of the factors involved.

The direction and extent of tax shifting is determined basically by one principle: The user of a tax object can avoid the tax burden to a greater (lesser) extent the easier (the more difficult) it is to find nontaxed or less-taxed alternatives or substitutes for the tax object; the supplier of a production factor that is taxed or used in the production of a taxed good can avoid the tax burden to a greater (lesser) extent the easier (the more difficult) it is to find equivalent nontaxed or less taxed alternative employment opportunities for this factor. Because the demand for substitute goods will increase, their prices may rise, thus benefiting the producers of such goods and placing part of the tax burden on those individuals who used them before the tax was imposed. Likewise, the productive factors that seek alternative employments to avoid the tax will tend to receive lower returns in those employments, thus placing part of the burden on individuals who supplied the factors in those sectors before the tax was imposed. For example, if wine is taxed while beer is not, then—if these two beverages are regarded as perfect substitutes and the price of beer does not rise with increased demand—the tax burden will fall on the owners of land used for viticulture and on the workers engaged in it. It will fall mainly on the landowners if the soil is specific to grapevine growing and if labour has alternative employment possibilities. If, on the other hand, wine drinkers are determined to drink only wine, they will bear most of the tax burden. If some substitution of beer for wine takes place and the price of beer rises somewhat, both wine and beer drinkers will bear the burden and owners of resources specialized to the production of beer will benefit.

In addition to the substitution effect discussed above, one must take into account the income effect. When taxation reduces real income, consumption of certain goods and services (and of leisure) will be reduced, because people have less money to spend. Furthermore, if a tax causes a significant redistribution of real income and if different income classes have different propensities to save and different patterns of consumption, then the income redistribution will influence the demand for various goods, the supply of labour, and the demand for various resources.

Other considerations affect tax shifting, but they are derived from the basic principle of substitution. The extent of shifting may vary over time, depending on how long it takes to adjust consumption patterns, reallocate land and capital, retrain labour, and so on. Those users and suppliers who have the most difficulty in adjusting will bear the largest burden.

The breadth of the tax base affects tax incidence. The broader (narrower) the tax base—i.e., the more (less) inclusive the scope of the tax—the more difficult it is to escape the tax burden, since the range of nontaxed or less-taxed substitutes is narrower (wider). Thus, an excise tax on only a few alcoholic beverages allows the tax to be escaped through a change in the consumption pattern, while a tax on all such beverages does not. In a similar fashion, the returns on capital will be affected less by the taxation of corporation profits alone than by the taxation of both corporation and noncorporation profits.

The smaller the jurisdictional unit imposing the tax, the easier it tends to be for a user to obtain nontaxed or less-taxed substitutes from outside the jurisdiction and for a supplier to find nontaxed or less-taxed outside employment opportunities for his goods and services. Thus, a tax levied by a subnational government on the production of a particular good is likely to be borne by suppliers of commodities and productive factors that are immobile. This is particularly relevant to the determination of the incidence of state income taxes and local property taxes, taxes that are often thought to be “exported” to out-of-state consumers. In small communities the only really immobile factors are likely to be real estate, certain local services, and perhaps poor families.

The rigidities of imperfect markets are likely to increase the uncertainty of the shifting response. Thus, a monopolist may absorb part of a tax in lower profits rather than shift all of the burden to the user of the product. In industries where there are few firms (oligopoly), the price behaviour of a firm is mainly determined by what it expects its competitors to do. It may be especially easy for regulated public utilities to shift taxes forward. Rigid product prices are likely to increase the incidence of taxes on employment, unless monetary policy allows the tax-induced changes in relative prices to take place in the setting of a generally rising price level.

All of these considerations are analytical and theoretical. Efforts have been made to measure the impact of taxation by studying the actual effects of a particular tax on income and employment. These studies reflect the obvious and inherent difficulty that the tax impact cannot be easily isolated from the economic consequences of other events. For example, studies of corporate income tax shifting vary in their results, from the conclusion that the tax is not shifted at all to the conclusion that it is shifted by more than 100 percent, depending mainly on the methods used to isolate the tax impact.

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